Recently, with the increase of crimes typified by picking, robbery, arson, and the like, the popularity of a video monitoring system in which cameras, sensors, storage devices, and the like are disposed to prevent crimes is largely expanding. In accordance with adoption of IP to a monitoring camera and the increasing of the capacity of a storage device, the number of systems which perform wide-area monitoring of several hundred devices and long-time recording is increased. Under these circumstances, in order to reduce the task of an observer, it has been requested to develop a technique for efficiently sorting out a specific person such as a shoplifter, a lost child, or a person who has lost an article.
As a conventional technique for sorting out a specific person at high speed, there is a technique in which a group of multidimensional feature data (a face, a color, and the like) extracted from an image is previously clustered in ascending order of distance to be formed as a tree structure, and, in a searching process, only a subtree which is closest to the person to be searched is subjected to the searching process. Patent Reference 1 discloses a method in which projection is performed in a model space that is prepared by a statistical technique, and multidimensional feature data that are highly accurate, and that have a reduced number of dimensions are produced, thereby performing a high-speed search.    Patent Reference 1: JP-A-2002-183205